I'd post links to my blog, but Photobucket removed the pics, so I'll try and answer the questions the best I can until I can run some more AAR's.
TOD gives you several options for running Zed Stars. You can either play the scenarios in the book (Each scenario includes rules and background info for the zombies). You can also play the encounters in FFO; TOD includes rules for flipping the script on these. In addition, you can control either normal zombies or Special Zeds which are more powerful.
As for how they play out, the encounters in FFO play out in various manners. The scenarios in TOD however can be extremely easy, especially if you're playing as a Special Zed. For example, when playing the Bloody Big Top scenario, I won every single time as the zeds. Even when I only controlled Giggles, the zombie clown, I still massacred the humans. Granted you can make things challenging by adding more humans or giving them bigger guns, but that's up to you. I didn't want to create a constant balance for Zed Stars as I figured some people may just want to control zombies for kicks or to blow off steam.
Finally, although rules for improving your zed star exist, those campaigns may not last long, as zeds don't normally interact with others as humans do. You can still play out a campaign, but your zed will probably be just eating a lot of humans.
Mostly I created the option because I love playing as the monster sometimes.
Hope that helps.